The effects of vasodilators on blood flow and tissue oxygen delivery have been studied previously at the level of whole organs and tissues. Results have indicated that some vasodilators, wile increasing tissue blood flow, do not appear to increase tissue oxygenation. The usual mechanism invoked to account for this paradoxical behavior is a redistribution of blood flow from nutritive to non-nutritive channels. We propose to investigate this problem from the standpoint of the microvascular changes which occur during the action of various vasodilator drugs. These studies will be conducted on the suffused hamster cheek pouch and cremaster muscle preparations which allow both topical application and intravascular infusion of drugs. The microcirculation will be visualized and recorded using a closed circuit video system and the action of vasodilators on these preparations will be characterized qualitatively and quantitatively. Recordings of vascular diameter, local oxygen tension, percent blood oxygen saturation and red cell velocity will be used to compute changes in oxygen delivery and tissue oxygenation induced by the vasodilator drugs. Vascular diameter and red cell velocity will be determined optically, oxygen tension will be obtained polarographically with oxygen microcathodes and percent oxyhemoglobin will be obtained by a new video densitometer technique. Where possible, local oxygen uptake will be calculated by applying Fick's principle to a functional microcirculatory exchange unit consisting of a feeding arteriole, capillary bed and collecting venule. We will also apply our microvascular findings in a brief collaborative study of a whole tissue system, the isolated dog gracilis muscle. Measurements of blood flow and oxygen uptake will be obtained and compared with our preceding results. Both the microvascular and whole tissue studies should provide information regarding microvascular oxygen transport and the effect of vasodilators on tissue oxygen delivery and offer suggestions concerning vasodilator drug therapy in coronary and peripheral vascular disease states.